In the related art, since a capacitive fingerprint detection circuit in a chip has advantages of small size and low power consumption, this kind of the fingerprint detection circuit is more preferred in the mobile phone and tablet market
Such fingerprint detection circuit detects fingerprint ridge information and fingerprint valley information. Since the distance between the fingerprint ridge and a sensing unit of the fingerprint detection unit is relatively small, and the distance between the fingerprint valley and the sensing unit of the fingerprint detection unit is relatively large, there is a difference between a ridge capacitance generated between the fingerprint ridge ridge the sensing unit and a valley capacitance generated between the fingerprint valley and the sensing unit. Once the ridge capacitance and the valley capacitance (referred to finger capacitance hereinafter) are detected, ridge characteristics and valley characteristics of the finger may be analyzed.
An output voltage output from the above fingerprint detection circuit has a proportional linear relationship with the finger capacitance (capacitance to be tested). A final result has a small difference between an output voltage corresponding to the finger capacitance of the ridge and an output voltage corresponding to the finger capacitance of the valley, so that it needs to amplify an output voltage corresponding to the finger capacitance by a predetermined factor for processing. However, the amplified factor can be limited by a range, if the amplified factor is too large, the output voltage will exceed the range to cause the data to overflow, if the amplified factor is too small, and the calculated difference between the output voltage corresponding to the finger capacitance of the ridge and the output voltage corresponding to the finger capacitance of the valley is too small, which is too difficult to identify, and the finger detection result cannot be optimized.